Sasha CampbellThose tiny bumps on your plants may be scale insects.
Scale insects feed on plant fluids. A large number of them can weaken a plant. The leaves may turn yellow, wilt, or fall early. Severe infestations may also cause poor growth and dying branches.
Most healthy plants can handle a small number of scale insects. However, early control can prevent the pests from spreading.
Identification
Scale insects are small pests that often look like shells, scabs, or bumps. You may find them on stems, branches, leaves, and fruit. They can be white, gray, brown, yellow, or black.
The two main groups are soft scales and armored scales.
Soft scales often have round or raised bodies. They make a sweet, sticky liquid called honeydew. This liquid may attract ants and cause black sooty mold to grow.
Armored scales have a hard cover that protects their bodies. They do not make honeydew. Their covers may be round, oval, or shaped like tiny oyster shells [1].
Young scale insects are called crawlers. They have legs and move around the plant. After finding a feeding spot, many of them settle down and stop moving.
Crawlers are easier to control than adult scales because they do not yet have thick protective covers.
How to Tell if Scale Insects Are Alive
Old scale covers may stay on a plant after the insects die. This can make it seem as if a treatment did not work.
Gently scrape off one scale and look beneath it. A living scale often has a soft or moist body. A dead one may look dry or empty.
This test is not always exact. Continue watching the plant for crawlers, new scales, and signs of damage.
Do not mistake natural bumps, buds, or marks on the bark for scale insects. If you are unsure, ask a local garden expert to help identify the pest.
Signs of a Scale Infestation
Common signs include:
- Small bumps on stems, leaves, or branches
- Yellow or spotted leaves
- Leaves falling early
- Slow or weak growth
- Wilting
- Dying twigs or branches
- Sticky honeydew from soft scales
- Black sooty mold
- Ants crawling over the plant
Honeydew and sooty mold usually point to soft scale or another pest that feeds on plant fluids. Armored scales do not make honeydew.
How to Get Rid of Scale on Plants Naturally
The best treatment depends on the type of scale and the plant it is feeding on. Start with simple methods. Use a pesticide only if the infestation is causing noticeable damage.
Safety tip: Always read and follow the product label. Make sure the product is approved for the plant and the place where you plan to use it. A product labeled for outdoor ornamental plants may not be safe for houseplants or edible crops.
1. Rub Them Off
Removing scale insects by hand works well on houseplants and small garden plants.
Use your fingernail, a toothpick, a cotton swab, or a soft toothbrush. Gently scrape the scales from the stems and leaves. Be careful not to damage the plant.
Check beneath leaves, along leaf veins, and where leaves join the stem. Scale insects often hide in these places.
Removing them quickly lowers the number of pests. It also makes it easier to spot new scales later. The University of Maryland recommends this method for scale insects on indoor plants [2].
Check the plant once a week and remove any scales you find.
2. Prune Heavily Infested Parts
Prune branches or leaves that are covered with scale insects. This can quickly reduce a large infestation.
Do not remove too much of the plant at once. Heavy pruning can place more stress on an unhealthy plant.
Place infested plant parts in the trash or move them far away from the growing area. Do not leave them beside healthy plants.
If a small houseplant is badly infested and does not improve, it may be best to discard it. This can stop the pests from spreading to other plants.
3. Apply Horticultural Oil
Horticultural oil is one of the most useful treatments for scale insects. It works by covering and smothering the pests.
Choose a commercial horticultural oil labeled for the plant you want to treat. Do not use a homemade mixture of vegetable oil and soap. Homemade oil sprays may burn or damage leaves.
Cover the stems, branches, and both sides of the leaves. Good coverage is important because the oil must touch the pests to work.
Some oils are used when trees are dormant. Others can be used during the growing season when crawlers are active. Always follow the product label because plants and oil products differ.
Do not spray a dry, wilted, or heat-stressed plant. Avoid using oil during very hot weather unless the label says it is safe.
Test the product on a small part of the plant first. Wait as long as the label recommends before treating the entire plant.
4. Use Insecticidal Soap
Insecticidal soap can help control crawlers and some young soft scale insects. It does not work as well on adult armored scales because their hard covers protect them.
Buy a product labeled as insecticidal soap. Dish detergent and homemade Castile soap sprays are not the same. Household soaps may damage the protective surface of plant leaves.
Cover the scale insects and crawlers well. Spray only as much as the label directs. The soap must touch the pests to work.
More than one treatment may be needed. Follow the label for mixing, timing, and repeat applications.
5. Use a Labeled Neem Oil Product
Neem oil may help control scale insects, especially crawlers and young scales. The oil works best when it completely covers the pests.
Use a neem product labeled for the affected plant and scale insects. Follow the mixing rate printed on the package instead of using a general homemade recipe.
Spray in the early morning or evening. Do not spray open flowers or apply the product while bees are visiting the plant.
Test the spray on a few leaves first. Wait as long as the label recommends to check for damage before treating the whole plant.
6. Protect Beneficial Insects
Lady beetles, lacewings, predatory bugs, and tiny parasitic wasps feed on many types of scale insects. These helpful insects may keep a light infestation under control [3].
Avoid broad insect sprays that kill many kinds of insects. These products may kill the natural enemies of scale and allow the infestation to become worse.
Grow small flowers that provide pollen and nectar. Yarrow, sweet alyssum, dill, and cosmos may help attract beneficial insects.
Buying beneficial insects does not always solve the problem. The helpful insect must match the type of scale and the growing conditions. Protecting the beneficial insects already in your garden is often easier.
7. Control Ants Around the Plant
Ants feed on the sweet honeydew made by soft scales. They may protect the scales from lady beetles and other natural enemies.
Watch for ants traveling up and down the plant. Prune branches that touch walls, fences, or nearby plants. These branches can act like bridges for ants.
For trees, place a protective wrap around the trunk before applying a sticky barrier. Do not place the sticky material directly on the bark. Follow the product directions to avoid harming the tree.
Controlling ants allows predators and parasitic wasps to reach the scale insects more easily.
8. Watch for Crawlers
Treatments often work best when crawlers are active. These young scales are tiny, so they can be hard to see.
Wrap double-sided tape around an infested twig. You can also wrap regular tape around the twig with the sticky side facing outward.
Check the tape often with a magnifying glass. Tiny yellow, orange, or pale insects stuck to it may be crawlers.
Crawler timing depends on the scale species and local weather. Some scales have one crawler period each year. Others may produce several generations.
Because crawlers do not all hatch at once, you may need more than one treatment. Follow the pesticide label instead of using the same schedule for every plant.
How to Prevent Scale Insects
Inspect plants carefully before buying them. Check the stems, leaf veins, leaf undersides, and places where leaves meet the stem.
Keep new houseplants away from your other plants at first. Watch them for scale insects, sticky leaves, or yellowing before placing them with the rest of your collection.
Give each plant the right amount of light, water, and fertilizer. Plant stress does not create scale insects, but a weak plant may suffer more damage from them.
Avoid using too much nitrogen fertilizer. It can cause large amounts of soft new growth.
Check plants regularly. Finding a few scales early is much easier than treating a heavy infestation.
Keep ants under control and protect helpful insects. Avoid broad insecticides unless they are truly needed.
Frequently Asked Questions
Will Dawn Dish Soap Kill Scale Insects?
Dish soap may kill some exposed crawlers, but it can also burn or damage plant leaves. It is not made or tested for use as a plant pesticide.
A commercial insecticidal soap labeled for the plant is a safer choice.
What Causes Scale Insects on Plants?
Scale insects often enter a home or garden on an infested plant. Crawlers can move to nearby leaves and plants. Some may also be carried by wind.
Poor plant care does not create scale insects. However, an unhealthy plant may be less able to handle their feeding.
Can a Plant Recover From Scale Insects?
Yes. Many plants recover when the pests are found and controlled early.
Remove badly damaged growth and continue checking the plant for new crawlers. Give the plant the correct light, water, and nutrients while it recovers.
Are Scale Insects Harmful to People?
Scale insects do not bite or sting people. They do not damage homes. They are pests because they feed on plants.
What Plants Do Scale Insects Attack?
Different scale insects feed on different plants. Possible hosts include houseplants, citrus trees, fruit trees, shrubs, palms, orchids, hibiscus, camellias, and many ornamental plants.
Some scale species feed on only a few types of plants. Others can attack hundreds of different plants.
Does Neem Oil Kill Scale Insects?
Neem oil may control some scales when it completely covers them. It often works best on crawlers and young scales.
Adult armored scales are harder to kill because their covers protect them. Good coverage and repeat treatments may be needed.
What Is the Fastest Way to Remove Scale Insects?
For a light infestation, scraping or brushing the scales off gives the fastest visible result.
For a heavy infestation, prune badly affected parts. Then use a labeled horticultural oil, neem product, or insecticidal soap if needed.
How Often Should I Treat a Plant for Scale?
There is no single schedule that works for every scale insect or pesticide.
Check the product label. Monitor the plant for crawlers and new scale growth. Several treatments may be needed because the eggs do not all hatch at the same time.
Takeaway
Scale insects may look like harmless bumps, but large numbers can weaken plants. Soft scales may also leave sticky honeydew that leads to black sooty mold.
Start by removing the pests by hand or pruning badly infested growth. Protect beneficial insects and control ants. If more treatment is needed, use a horticultural oil, neem product, or insecticidal soap labeled for your plant.
Check the plant regularly after treatment. Early action makes scale insects much easier to manage.
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I have hard scale insects on my water lilies in the koi pond. They are on the lily pads and stems. How did this happen and how to get rid of them?